U.S. patent application number 13/978489 was filed with the patent office on 2013-10-31 for liquid crystal display device.
This patent application is currently assigned to SHARP KABUSHIKI KAISHA. The applicant listed for this patent is Yusuke Masuda. Invention is credited to Yusuke Masuda.
Application Number | 20130285994 13/978489 |
Document ID | / |
Family ID | 46458634 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130285994 |
Kind Code |
A1 |
Masuda; Yusuke |
October 31, 2013 |
LIQUID CRYSTAL DISPLAY DEVICE
Abstract
A liquid crystal display device includes: a display control unit
configured to cause the liquid crystal panel to display a right eye
image and a left eye image in an alternating manner; and a polarity
control unit configured to cause the polarity of the drive voltage
for the liquid crystal panel to be reversed. The polarity control
unit causes the polarity of the drive voltage to be reversed such
that, in one cycle including a number of display frames for right
and left eye images, the number being a multiple of 8, the
combination of polarities for image display in one pair of display
frames composed of right and left eye images is one of four
combinations and a number of occurrences of each of the four
combinations is equal.
Inventors: |
Masuda; Yusuke; (Osaka-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Masuda; Yusuke |
Osaka-shi |
|
JP |
|
|
Assignee: |
SHARP KABUSHIKI KAISHA
Osaka-shi, Osaka
JP
|
Family ID: |
46458634 |
Appl. No.: |
13/978489 |
Filed: |
January 5, 2012 |
PCT Filed: |
January 5, 2012 |
PCT NO: |
PCT/JP2012/050096 |
371 Date: |
July 5, 2013 |
Current U.S.
Class: |
345/209 ;
345/87 |
Current CPC
Class: |
G09G 3/3648 20130101;
H04N 13/398 20180501; H04N 13/341 20180501; G09G 3/003 20130101;
G02B 30/24 20200101; G09G 5/14 20130101; G09G 3/3614 20130101 |
Class at
Publication: |
345/209 ;
345/87 |
International
Class: |
G09G 5/14 20060101
G09G005/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 6, 2011 |
JP |
2011--001032 |
Claims
1. A liquid crystal device comprising: a liquid crystal panel
configured to display an image; a display control unit configured
to cause the liquid crystal panel to display a right eye image to
be viewed by a right eye of a viewer and a left eye image to be
viewed by a left eye of the viewer in an alternating manner; and a
polarity control unit configured to cause a polarity of a drive
voltage for the liquid crystal panel to be reversed, wherein the
polarity control unit causes the polarity of the drive voltage to
be reversed such that, in one cycle including a number of display
frames for right and left eye images, the number being a multiple
of 8, a combination of polarities for image display in one pair of
display frames composed of right and left eye images is one of four
combinations and a number of occurrences of each of the four
combinations is equal.
2. The liquid crystal display device according to claim 1, wherein
the polarity control unit reverses the polarity of the drive
voltage such that, in the one cycle, the number of occurrences of
switching a display from a left eye image to a right eye image and
the number of occurrences of switching the display from a right eye
image to a left eye image remain the same whether the polarity of
the drive voltage remains the same or changes.
3. The liquid crystal display device according to claim 1, wherein
the polarity control unit reverses the polarity of the drive
voltage such that the one cycle includes eight consecutive display
frames and that the combination of polarities for image display in
the one pair of display frames is one of the four combinations on a
one-to-one basis.
4. The liquid crystal display device according to claim 1, wherein
each of the display frames includes two frames having an identical
polarity and displaying an identical image.
Description
TECHNICAL FIELD
[0001] The present invention relates to liquid crystal display
devices including a liquid crystal panel that is capable of
displaying a right eye image and a left eye image in an alternating
manner.
BACKGROUND ART
[0002] Liquid crystal display devices including a liquid crystal
panel that is capable of displaying a right eye image and a left
eye image in an alternating manner are known. In such a liquid
crystal display device, as disclosed in JP 2009-75392 A, for
example, polarity reversion may be performed, i.e. the polarity of
the voltage applied to the liquid crystal of the liquid crystal
display device may be reversed to prevent the polarity of the
voltage applied to the liquid crystal from being the same
continuously.
[0003] More specifically, the arrangement disclosed in JP
2009-75392 A prevents the voltage polarity from being the same
continuously when right and left eye images are displayed by
changing the polarity of the voltage applied to the liquid crystal
at an interval of two frames composed of right and light eye
images. This prevents image sticking in, and deterioration of, the
liquid crystal caused by imbalances in the voltage applied to the
liquid crystal in terms of polarity, for example.
DISCLOSURE OF THE INVENTION
[0004] In the arrangement disclosed in JP 2009-75392 A, the amount
of change in the voltage necessary to achieve a prescribed voltage
when the display is switched between a right eye image and a left
eye image differs depending on whether the polarity of the voltage
applied to the liquid crystal (i.e. the drive voltage) is changed
or not. That is, switching between a right eye image and a left eye
image while the polarity of the drive voltage remains the same does
not require a large amount of change in the voltage. On the other
hand, switching between a right eye image and a left eye image when
the polarity of the drive voltage changes requires a larger amount
of change in the voltage due to a polarity change.
[0005] Consequently, when the display is switched between a right
eye image and a left eye image, the voltage actually applied to the
liquid crystal varies depending on whether the polarity of the
drive voltage remains the same or is reversed, resulting in
variations in the response waveform of the liquid crystal. This may
result in variations in the display quality of three-dimensional
(3D) images.
[0006] The object of the present invention is to provide a liquid
crystal display device including a display panel that is capable of
displaying a right eye image and a left eye image in an alternating
manner where the variation in the response waveform of the liquid
crystal when the display is switched between a right eye image and
a left eye image is reduced while preventing image sticking in the
liquid crystal caused by imbalances in the drive voltage in terms
of polarity.
[0007] A liquid crystal display device according to an embodiment
of the present invention includes: a liquid crystal panel
configured to display an image; a display control unit configured
to cause the liquid crystal panel to display a right eye image to
be viewed by a right eye of a viewer and a left eye image to be
viewed by a left eye of the viewer in an alternating manner; and a
polarity control unit configured to cause a polarity of a drive
voltage for the liquid crystal panel to be reversed, wherein the
polarity control unit causes the polarity of the drive voltage to
be reversed such that, in one cycle including a number of display
frames for right and left eye images, the number being a multiple
of 8, a combination of polarities for image display in one pair of
display frames composed of right and left eye images is one of four
combinations and a number of occurrences of each of the four
combinations is equal.
[0008] The liquid crystal display device according to one
embodiment of the present invention reduces the variation in the
response waveform of the liquid crystal when the display is
switched between a right eye image and a left eye image while
preventing image sticking in the liquid crystal caused by
imbalances in the drive voltage in terms of polarity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a block diagram schematically illustrating a
liquid crystal display device according to an embodiment of the
present invention.
[0010] FIG. 2 schematically illustrates a portion of the
active-matrix substrate.
[0011] FIG. 3 illustrates an example of a pattern of changes in the
drive voltage encountered when the polarity of the drive voltage is
reversed at an interval of a pair of display frames composed of
right and left eye images.
[0012] FIG. 4 illustrates another example of a pattern of changes
in the drive voltage encountered when the polarity of the drive
voltage is reversed at an interval of a pair of display frames
composed of right and left eye images.
[0013] FIG. 5 illustrates (A) an enlarged graph of a portion of the
example of a pattern of changes in the drive voltage shown in FIG.
3 and (B) a corresponding response waveform of the liquid
crystal.
[0014] FIG. 6 illustrates (A) an enlarged graph of a portion of the
example of a pattern of changes in the drive voltage shown in FIG.
4 and (B) a corresponding response waveform of the liquid
crystal.
[0015] FIG. 7 illustrates a deviation in brightness encountered
when the response waveform of the liquid crystal is distorted.
[0016] FIG. 8 illustrates an example of a pattern of changes in the
drive voltage that uses all the four possible combinations of drive
voltage polarities in one cycle.
[0017] FIG. 9 illustrates (A) changes in the drive voltage in the
example of a pattern of changes in the drive voltage shown in FIG.
8 and (B) a corresponding response waveform of the liquid
crystal.
[0018] FIG. 10 illustrates how the deviation in brightness is
reduced when the drive voltage is changed as shown in FIG. 8.
[0019] FIG. 11 illustrates another example where all the four
possible combinations of drive voltage polarities are used in one
cycle, similar to FIG. 8.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0020] A liquid crystal device according to one embodiment of the
present invention includes: a liquid crystal panel configured to
display an image; a display control unit configured to cause the
liquid crystal panel to display a right eye image to be viewed by a
right eye of a viewer and a left eye image to be viewed by a left
eye of the viewer in an alternating manner; and a polarity control
unit configured to cause a polarity of a drive voltage for the
liquid crystal panel to be reversed, wherein the polarity control
unit causes the polarity of the drive voltage to be reversed such
that, in one cycle including a number of display frames for right
and left eye images, the number being a multiple of 8, a
combination of polarities for image display in one pair of display
frames composed of right and left eye images is one of four
combinations and a number of occurrences of each of the four
combinations is equal (first arrangement).
[0021] In the above arrangement, in one cycle including a number of
display frames for right and left eye images, the number being a
multiple of 8, the combinations of drive voltage polarities, each
in one pair of display frames composed of right and left eye
images, include all the four possible combinations and the number
of occurrences of each of the four combinations is equal. Thus,
within one such cycle, the number of occurrences of the positive
polarity of the drive voltage for right and left eye images is the
same as that of the negative polarity, thereby preventing the drive
voltage from being unbalanced toward one polarity.
[0022] Further, in the above arrangement, the number of occurrences
of switching between a right eye image and a left eye image when
the drive voltage polarity changes is substantially equal to the
number of occurrences of switching between a right eye image and a
left eye image while the drive voltage polarity remains the same.
This will reduce the variation in the amount of change in the
voltage caused by a change in the drive voltage polarity, thereby
reducing the variation in the response waveform of the liquid
crystal.
[0023] Thus, the above arrangement will improve the display quality
of 3D images while preventing image sticking in the liquid crystal
caused by imbalances in the drive voltage in terms of polarity, for
example.
[0024] Typically, in a liquid crystal display device, a
predetermined gray scale display is achieved by applying to the
liquid crystal a voltage greater than the level required to drive
the liquid crystal (i.e. an overshoot voltage). Accordingly, when
there are variations in the amount of change in the voltage until
the voltage reaches a prescribed value due to changes in the
polarity of the drive voltage, the overshoot voltage must be
changed as well, requiring memory space for storing the associated
correction values. In contrast, the above arrangement reduces the
variation in the amount of change in the voltage and thereby
prevents an increase in the memory space.
[0025] Display frame as used herein means one left or right eye
image. Consequently, when an identical right or left eye image is
displayed a plurality of times, one such right or left eye image is
one display frame.
[0026] In the first arrangement, it is preferable that the polarity
control unit reverses the polarity of the drive voltage such that,
in the one cycle, the number of occurrences of switching a display
from a left eye image to a right eye image and the number of
occurrences of switching the display from a right eye image to a
left eye image remain the same whether the polarity of the drive
voltage remains the same or changes (second arrangement).
[0027] This will reduce the variation in the amount of change in
the voltage caused by changes in the drive voltage polarity,
thereby reducing the variation in the response waveform of the
liquid crystal. This will improve the display quality of 3D
images.
[0028] In the first or second arrangement, it is preferable that
the polarity control unit reverses the polarity of the drive
voltage such that the one cycle includes eight consecutive display
frames and that the combination of polarities for image display in
the one pair of display frames is one of the four combinations on a
one-to-one basis (third arrangement).
[0029] Thus, as the smallest number of display frames is provided,
an arrangement will be achieved where imbalances in the drive
voltage in terms of polarity are eliminated and the variation in
the amount of change in the voltage caused by a change in the
polarity is reduced. While larger numbers of display frames would
make the signal more complicated when the polarity of the drive
voltage is switched, providing the smallest number of display
frames will prevent the signal from being complicated.
[0030] In any one of the first to third arrangements, it is
preferable that each of the display frames includes two frames
having an identical polarity and displaying an identical image
(fourth arrangement).
[0031] Now, preferred embodiments of the liquid crystal display
device of the present invention will be described with reference to
the drawings. The dimensions of the components in the drawings do
not exactly represent the dimensions of the actual components or
the size ratios of the components.
[0032] (Overall Configuration)
[0033] FIG. 1 shows a block diagram schematically illustrating a
liquid crystal display device 1 according to an embodiment of the
present invention. The liquid crystal display device 1 includes a
liquid crystal panel 11, backlight 12, gate driver 13, source
driver 14 and control device 20. As detailed below, the liquid
crystal display device 1 is configured to allow a viewer using
stereoscopic glasses 30 to perceive 3D images. The liquid crystal
display device 1 may be used as the display unit of, for example, a
television, game machine, personal computer, personal digital
assistant, or the like.
[0034] Although not shown, the liquid crystal panel 11 includes an
active-matrix substrate, a counter substrate located opposite the
active-matrix substrate, and a liquid crystal layer enclosed
between these two substrates. The liquid crystal panel 11 may be a
transmissive liquid crystal panel, for example, or a reflective or
semireflective liquid crystal panel. That is, the liquid crystal
panel 11 may be in any configuration as long as it is capable of
displaying images.
[0035] As shown in FIG. 2, the active-matrix substrate includes a
thin-film transistor 15 that serves as a switching device, a pixel
electrode 16, and a plurality of gate lines 17 and a plurality of
source lines 18 arranged as a grid to surround the transistor and
pixel electrode.
[0036] As shown in FIG. 2, the thin-film transistor 15 on the
active-matrix substrate has a gate electrode connected with a gate
line 17. The thin-film transistor 15 has a source electrode
connected with a source line 18. Further, the thin-film transistor
15 has a drain electrode connected with the pixel electrode 16.
[0037] Although not shown, the counter substrate is located
opposite the active-matrix substrate at least at the pixel
electrodes 16. The counter substrate includes a common electrode. A
charge accumulating capacitance for accumulating a charge is formed
by the common electrode, the pixel electrode 16 on the
active-matrix substrate and the liquid crystal layer, not shown,
located between the common and pixel electrodes.
[0038] As shown in FIG. 1, the gate lines 17 are connected with the
gate driver 13. The gate driver 13 is configured to output a gate
control signal provided by the display control unit 22, discussed
below, to the gate lines 17 in the form of the gate voltage. The
gate driver 13 outputs the gate voltage in response to a vertical
synchronization signal provided by the display control unit 22. The
one of the gate lines 17 provided with the gate voltage by the gate
driver 13 transitions to a selected state.
[0039] As shown in FIG. 1, the source lines 18 are connected with
the source driver 14. The source driver 14 generates a gray scale
display signal necessary for the gray scale display of images based
on image data provided by the display control unit 22. Further, the
source driver 14 is configured to output the gray scale display
signal to the source lines 18 in the form of the drive voltage.
More specifically, the source driver 14 outputs a drive voltage
corresponding to the one of the gate lines 17 that is selected by
the gate driver 13. The source driver 14 outputs the drive voltage
in response to a horizontal synchronization signal provided by the
display control unit 22.
[0040] The source driver 14 is configured to set the polarity of
the drive voltage based on a polarity control signal provided by
the polarity control unit 23, as discussed below. More
specifically, the source driver 14 is configured to output a drive
voltage that is positive relative to the voltage of the common
electrode, discussed below (hereinafter referred to as common
voltage) and a drive voltage that is negative relative to the
common voltage at a predetermined interval based on the polarity
control signal. This prevents image sticking in the liquid crystal
caused by a voltage of one polarity being continuously applied to
the liquid crystal.
[0041] Although not shown, the backlight 12 is located adjacent one
of the two sides of the liquid crystal panel 11 disposed in a
thickness direction. The backlight 12 may be, for example, a direct
backlight, an edge light or a flat surface light source. The light
source for the backlight 12 may be a cold-cathode tube or a
light-emitting diode, for example.
[0042] The control device 20 may include a synchronization control
unit 21, display control unit 22, polarity control unit 23 and
glasses control unit 24. Each of the synchronization control unit
21, display control unit 22, polarity control unit 23 and glasses
control unit 24 may be implemented by an integrated circuit, for
example. In implementations where the control unit 20 includes a
central processing unit and memory, for example, the
synchronization control unit 21, display control unit 22, polarity
control unit 23 and glasses control unit 24 are implemented by the
central processing unit reading a program stored in the memory and
executing it.
[0043] The synchronization control unit 21 is configured to provide
a synchronization reference signal to the display control unit 22,
polarity control unit 23 and glasses control unit 24. The
synchronization reference signal is a reference signal in response
to which the polarity of the drive voltage provided by the source
driver 14 to the source line 18 is reversed. In the present
embodiment, the frequency of the synchronization reference signal
is 240 Hz. The frequency of the synchronization reference signal is
not limited to 240 Hz and may be 120 Hz, for example.
[0044] The display control unit 22 is configured to provide a
vertical synchronization signal to the source driver 14 in response
to the synchronization reference signal provided by the
synchronization control unit 21. The vertical synchronization
signal is used to drive the source driver 14.
[0045] The display control unit 22 is configured to generate image
data of right eye images and image data of left eye images based on
stereoscopic image data provided to the display control unit 22.
The display control unit 22 is configured to provide the image data
of stereoscopic images to the source driver 14 in response to the
synchronization reference signal provided by the synchronization
control unit 21.
[0046] In the present implementation, the display control unit 22
generates image data of right and left eye images; however, the
present invention is not limited to such a configuration, and image
data of right and left eye images may be input to the display
control unit 22. In such implementations, the display control unit
22 outputs the input image data of right and left eye images to the
source driver 14 without manipulating it.
[0047] The display control unit 22 is configured to provide a
horizontal synchronization signal to the gate driver 13 in response
to the synchronization reference signal provided by the
synchronization control unit 21. The horizontal synchronization
signal is used to drive the gate driver 13.
[0048] The display control unit 22 is configured to provide a gate
control signal to the gate driver 13 in response to the
synchronization reference signal provided by the synchronization
control unit 21. The gate control signal turns the relevant
thin-film transistor 15 on.
[0049] Further, the display control unit 22 is configured to
provide a left-right identification signal to the glasses control
unit 24 in response to the synchronization control signal provided
by the synchronization control unit 21. The left-right
identification signal indicates whether the liquid crystal panel 11
is displaying a right eye image or left eye image.
[0050] The polarity control unit 23 is configured to provide a
polarity control signal to the source driver 14 in response to the
synchronization reference signal provided by the synchronization
control unit 21. The polarity control signal sets the polarity of
the drive voltage. As discussed below, the polarity control unit 23
controls the polarity of the drive voltage in such a way that no
image sticking occurs in the liquid crystal and the display quality
of 3D images is improved.
[0051] The glasses control unit 24 is configured to control the
light permeability of the stereoscopic glasses 30. Although not
shown, the stereoscopic glasses 30 include a right eye liquid
crystal shutter to be located forward of the right eye of the
viewer when worn by the viewer, and a left eye liquid crystal
shutter to be located forward of the left eye of the viewer. The
liquid crystal shutters may be implemented using liquid crystal
panels, for example.
[0052] The glasses control unit 24 is configured to control the
opening/closing of the right and left eye liquid crystal shutters
of the stereoscopic glasses 30 in response to the synchronization
reference signal provided by the synchronization control unit
21.
[0053] The glasses control unit 24 is configured to control the
opening/closing of the right and left eye liquid crystal shutters
of the stereoscopic glasses 30 based on the left-right
identification signal provided by the display control unit 22. More
specifically, when in the liquid crystal panel 11 the display
control unit 22 outputs a left-right identification signal
indicating that a right eye image is being displayed, the glasses
control unit 24 causes the right eye liquid crystal shutter of the
stereoscopic glasses 30 to be opened (i.e. light can pass
therethrough) and causes the left eye liquid crystal shutter to be
closed (i.e. light cannot pass therethrough). On the other hand,
when in the liquid crystal panel 11 the display control unit 22
outputs a left-right identification signal indicating that a left
eye image is being displayed, the glasses control unit 24 causes
the left eye liquid crystal shutter of the stereoscopic glasses 30
to be opened (i.e. light can pass therethrough) and causes the
right eye liquid crystal shutter to be closed (i.e. light cannot
pass therethrough).
[0054] In a liquid crystal display device 1 having the
above-described configuration, the display control unit 22 drives
the gate driver 13 and source drive 14 to cause the liquid crystal
panel 11 to display a right eye image and a left eye image in an
alternating manner. In the present embodiment, each right or left
eye image is displayed for two frames. That is, for right and left
eye images, the image of the first frame is the same as that of the
second frame. In the description below, for ease of explanation, a
time period during which an identical right or left eye image is
displayed will be referred to as one display frame. That is, in the
description below, one display frame means two frames where an
identical image is displayed with the same drive voltage
polarity.
[0055] (Switching of Drive Voltage Polarity)
[0056] In a liquid crystal display device 1 having the
above-described configuration, different images taking the parallax
of the two eyes into consideration are displayed as a right eye
image and a left eye image such that a stereoscopic image can be
perceived as the right eye views the right eye image and the left
eye views the left eye image. Thus, when the display is switched
between the right eye image and the left eye image, the gray scale
level of the portions of the images that are changed due to the
parallax varies.
[0057] In implementations using polarity reversion where the drive
voltage polarity is reversed reciprocally for a right eye image and
a left eye image, for example, one drive voltage polarity is always
applied when right eye images are displayed while the other drive
voltage polarity is always applied when left eye images are
displayed. In such implementations, the portions of right and left
eye images where the parallax produces different gray scale levels
have imbalances in the drive voltage in terms of polarity, which
may cause image sticking in the liquid crystal. Particularly, when
a static image is displayed, right and left eye images with the
same parallax are successively displayed in an extended period of
time, increasing the likelihood of image sticking in the liquid
crystal.
[0058] In view of this, as is the case with the above-described
conventional techniques, the drive voltage polarity may be changed
at an interval of a pair of display frames composed of right and
left eye images to prevent the drive voltage polarity from being
the same continuously when displaying right and left eye images.
Examples of drive voltage patterns in such implementations are
indicated by the solid lines in FIGS. 3 and 4. In the
implementations of FIGS. 3 and 4, where left eye images (indicated
by L) have a high gray scale level (for example, white in the
example shown) and right eye images (indicated by R) have a low
gray scale level (for example, black in the example shown), the
drive voltage polarity ("++++" and "----" in the circles in the
graphs) is changed at an interval of a pair of display frames for
right and left eye images. That is, in the examples of FIGS. 3 and
4, the drive voltage polarity is changed such that the polarity for
the two frames for right eye images is the same as that for the two
frames for left eye images. FIGS. 3 and 4 are only different in
each combination of a pair of display frames having a single drive
voltage polarity. Further, while the present embodiment illustrates
an implementation where right eye images have a high gray scale
level and left eye images have a low gray scale level, the opposite
may be the case. Furthermore, while in the present embodiment the
images with a high gray scale level are white and the images with a
low gray scale level are black, the images with a high gray scale
level and those with a low gray scale level may be color images or
intermediate color images.
[0059] In the implementation of FIG. 3, the amount of change in the
voltage necessary at the transition from an image with a low gray
scale level (i.e. a right eye image; hereinafter referred to as R)
to an image with a high gray scale level (i.e. a left eye image;
hereinafter referred to as L), indicated by a hollow arrow in the
graph, is larger than the amount of change in the voltage necessary
at the transition from an image with a high gray scale level (L) to
an image with a low gray scale level (R), indicated by a hatched
arrow in the graph. Thus, in the implementation of FIG. 3, the
amount of change in the voltage necessary for a change in the gray
scale level is unbalanced as it is larger at the transition from an
image with a low gray scale level (R) to an image with a high gray
scale level (L).
[0060] On the contrary, in the implementation of FIG. 4, the amount
of change in the voltage necessary at the transition from an image
with a high gray scale level (L) to an image with a low gray scale
level (R), indicated by a hatched arrow in the graph, is larger
than the amount of change in the voltage necessary at the
transition from an image with a low gray scale level (R) to an
image with a high gray scale level (L), indicated by a hollow arrow
in the graph. Thus, in the implementation of FIG. 4, in contrast to
that of FIG. 3, the amount of change in the voltage necessary for a
change in the gray scale level is unbalanced as it is larger at the
transition from an image with a high gray scale level (L) to an
image with a low gray scale level (R).
[0061] Thus, the amount of change in the voltage necessary for
switching between image gray scales significantly varies if each
combination of a pair of display frames having a single drive
voltage polarity is different.
[0062] Next, FIG. 5 shows the necessary amount of change in the
voltage at the transition from an image with a low gray scale level
(R) to an image with a high gray scale level (L) according to FIG.
3 and a response waveform of the liquid crystal for the same time
period. FIG. 6 shows the necessary amount of change in the voltage
at the transition from an image with a low gray scale level (R) to
an image with a high gray scale level (L) according to FIG. 4 and a
response waveform of the liquid crystal for the same time period.
In each of FIGS. 5 and 6, (A) shows a polarity control signal
(indicated by the solid line) and an actual change in the voltage
in the liquid crystal (indicated by the broken line), while (B)
shows a response waveform of the liquid crystal for the same time
period. In each of FIGS. 5(B) and 6(B), the vertical axis
represents the brightness of images, for example.
[0063] It will be apparent from FIGS. 5 and 6 that a difference in
each combination of a pair of display frames having a single drive
voltage polarity results in a significant difference in the
necessary amount of change in the voltage and also results in a
difference in the voltage actually applied to the liquid crystal.
That is, if there is a change in the drive voltage polarity at the
transition from an image with a low gray scale level (R) to an
image with a high gray scale level (L), as indicated by the solid
line in FIG. 5(A), the necessary amount of change in the voltage is
relatively large such that the voltage actually applied to the
liquid crystal does not easily reach a prescribed level, as
indicated by the thick broken line in FIG. 5(A). In contrast, if
there is no change in the drive voltage polarity at the transition
from an image with a low gray scale level (R) to an image with a
high gray scale level (L), as indicated by the solid line in FIG.
6(A), the necessary amount of change in the voltage is relatively
small such that the voltage actually applied to the liquid crystal
quickly reaches a prescribed level, as indicated by the thick
broken line in FIG. 6 (B).
[0064] Thus, if there is a change in each combination of a pair of
display frames having a single drive voltage polarity, the
necessary amount of change in the voltage varies significantly
depending on whether the transition from an image with a low gray
scale level (R) to an image with a high gray scale level (L) is
accompanied by a change in the drive voltage polarity. Although not
shown, the same applies to the transition from an image with a high
gray scale level (L) to an image with a low gray scale level
(R).
[0065] Consequently, in the implementations using polarity
reversion shown in FIGS. 3 and 4, the response waveform of the
liquid crystal at the transition from an image with a low gray
scale level (R) to an image with a high gray scale level (L) is
significantly different from the response waveform of the liquid
crystal at the transition from an image with a high gray scale
level (L) to an image with a low gray scale level (R), as shown in
FIGS. 5(B) and 6(B). Thus, the response waveforms of the liquid
crystal in these implementations do not have a rectangular but a
distorted shape, as shown in FIGS. 5(B) and 6(B).
[0066] Such a distortion in the response waveform of the liquid
crystal affects the brightness of the screen. That is, according to
the drive voltage waveform shown in FIG. 4, for example, the amount
of change in the voltage necessary at every transition from an
image with a low gray scale level (R) to an image with a high gray
scale level (L) is small, while the amount of change in the voltage
necessary at every transition from an image with a high gray scale
level (L) to an image with a low gray scale level (R) is relatively
large. Consequently, as shown in FIG. 7, a target gray scale level
is reached at transitions from an image with a low gray scale level
(R) to an image with a high gray scale level (L), while a target
gray scale level is not reached at transitions from an image with a
high gray scale level (L) to an image with a low gray scale level
(R). Thus, in the case of the waveform of the drive voltage shown
in FIG. 4, the gray scale level that is actually perceived
(indicated by the black circle in FIG. 7) is higher than the target
gray scale level (indicated by the white circle in FIG. 7). That
is, the screen actually appears brighter than targeted.
[0067] To mitigate such a distortion in the response waveform of
the liquid crystal, the present embodiment provides a polarity
control unit 23 configured in the following manner.
[0068] First, the polarity control unit 23 is configured to change
the combination of polarities of the drive voltage applied to the
liquid crystal at an interval of a pair of display frames composed
of right and left eye images (see FIG. 8). That is, the polarity
control unit 23 is configured to change the combination of drive
voltage polarities for displaying right and left eye images from a
pair of display frames to the next pair of display frames. For
example, the polarity control unit 23 controls the drive voltage
polarity that, if the drive voltage polarity in a given display
frame for a right eye image is positive and the drive voltage
polarity in the following display frame for a left eye image is
positive, then, in the next pair of display frames, the drive
voltage polarity in the display frame for a right eye image is
negative and the drive voltage polarity in the following display
frame for a left eye images is negative.
[0069] Further, the polarity control unit 23 controls the drive
voltage polarity such that one cycle of changes in the drive
voltage polarity is composed of eight display frames, i.e. four
consecutive pairs of display frames for right and left eye images
(corresponding to 16 frames since each image is displayed twice if
the frequency of the synchronization reference signal is 240 Hz, as
in the present embodiment), and this cycle is repeated. Then, the
polarity control unit 23 controls the drive voltage polarity such
that, within one such cycle, the combinations of drive voltage
polarities, each in a pair of display frames for right and left eye
images, include all the four possible combinations of polarities.
More specifically, there are four possible combinations of drive
voltage polarities in one pair of display frames for right and left
eye images, namely ++(positive and positive), -- (negative and
negative), +- (positive and negative) and -+ (negative and
positive) for right and left eye images. The positive control unit
23 controls the drive voltage polarity such that all these four
polarity combinations are included in one cycle of changes in the
polarity described above.
[0070] FIG. 8 shows an example of a cycle using all the four drive
voltage polarity combinations. As shown in FIG. 8, using all the
four drive voltage polarity combinations results in an equal number
of the arrows of each type in one cycle. That is, in one cycle, out
of the transitions from an image with a low gray scale level (R) to
an image with a high gray scale level (L), those with a change in
the drive voltage polarity (indicated by the longer hollow arrows
in FIG. 8) and those without a change in the polarity (indicated by
the shorter hollow arrows in FIG. 8) are in the same number.
Similarly, in one cycle, out of the transitions from an image with
a high gray scale level (L) to an image with a low gray scale level
(R), those with a change in the drive voltage polarity (indicated
by the longer hatched arrows in FIG. 8) and those without a change
in the polarity (indicated by the shorter hatched arrows in FIG. 8)
are in the same number. Further, in one cycle, out of the
transitions from an image with a low gray scale level (R) to an
image with a high gray scale level (L) and from an image with a
high gray scale level (L) to an image with a low gray scale level
(R), those with a change in the drive voltage polarity (indicated
by the longer arrows in FIG. 8) and those without a change in the
polarity (indicated by the shorter arrows in FIG. 8) are in the
same number.
[0071] Thus, in one cycle, the amounts of change in the voltage at
the transitions from an image with a low gray scale level (R) to an
image with a high gray scale level (L) are evened up as a whole
regardless of whether a transition is accompanied by a change in
the drive voltage polarity or not, thereby evening up imbalances in
the amount of change in the voltage. Similarly, the imbalances in
the amount of change in the voltage at the transitions from an
image with a high gray scale level (L) to an image with a low gray
scale level (R) are evened up as a whole.
[0072] Thus, even though the response waveform of the liquid
crystal is distorted microscopically at image changes, the
distortion of the response waveform of the liquid crystal is evened
up over one cycle at the transitions from an image with a low gray
scale level (R) to an image with a high gray scale level (L) and
the transitions from an image with a high gray scale level (L) to
an image with a low gray scale level (R). More specifically, as
shown in FIG. 9, the response waveform of the liquid crystal (FIG.
9(B)) for the changes in the drive voltage (FIG. 9(A)) within one
cycle includes two types of trapezoids shown in FIGS. 5(B) and
6(B). Then, if this waveform is evened up over one cycle, the
response change from an image with a low gray scale level (R) to an
image with a high gray scale level (L), represented by the height
in the waveform of FIG. 9(B), is equal to the response change from
an image with a high gray scale level (L) to an image with a low
gray scale level (R), represented by the height in the waveform of
FIG. 9(B) in one cycle. Thus, the response waveform of the liquid
crystal as viewed by the viewer has substantially no
distortion.
[0073] That is, as the drive voltage for the liquid crystal is
provided in a pattern as shown in FIG. 8, the imbalances in the
amount of change in the voltage at transitions from an image with a
low gray scale level (R) to an image with a high gray scale level
(L) are substantially equal to the imbalances in the amount of
change in the voltage at transitions from an image with a high gray
scale level (L) to an image with a low gray scale level (R). Thus,
as shown in FIG. 10 as an example, the image gray scale level as it
is perceived (indicated by the black circle in the graph), which
depends on the average brightness of images with a high gray scale
level (L), indicated by the upper one-dot chain line shown, and the
average brightness of images with a low gray scale level (R),
indicated by the lower one-dot chain line shown, is substantially
equal to the targeted gray scale level (indicated by the white
circle in the graph).
[0074] Thus, using all the four drive voltage polarity combinations
in one cycle, as discussed above, rectifies the imbalances in the
brightness, thereby improving the display quality of 3D images.
[0075] Moreover, the number of occurrences of each of the two
polarities is equal for the right eye images and left eye images in
one cycle, thereby preventing the drive voltage from being
unbalanced toward one polarity. That is, the drive voltage may be
prevented from being unbalanced toward one polarity when displaying
right eye images, while the drive voltage may be prevented from
being unbalanced toward the other polarity when displaying left eye
images. Thus, the above arrangement will prevent image sticking in
the liquid crystal.
[0076] Further, the above arrangement will prevent the drive
voltage from being unbalanced in terms of polarity and reduce
imbalances in the amount of change in the voltage necessary to
change the gray scale level even when the images with a high gray
scale level (L) and the images with a low gray scale level (R) in
FIG. 8 are interchanged, for example. That is, even when the images
with a high gray scale level and the images with a low gray scale
level are interchanged, each combination of polarities is one of
the four possible combinations in one cycle and the number of
occurrences of each combination is the same, achieving the same
advantages as in FIG. 8.
[0077] If one or more of the four drive voltage polarity
combinations are not used in one cycle, the number of occurrences
of each type of voltage change will not be equal, as discussed
above (as in the implementations of FIGS. 3 and 4, for example) or,
even if the number of occurrences of each type of voltage change is
made equal, there will be imbalances in the voltage in terms of
polarity (for example, if the polarities for four display frames
are +++-). As such, an arrangement that prevents the drive voltage
from being unbalanced in terms of polarity and evens up the
imbalances in the amount of change in the voltage can only be
achieved by using all the four polarity combinations, as in the
present embodiment.
[0078] The drive voltage polarity combinations in one cycle are not
limited to the above-described pattern of FIG. 8 as long as all the
four polarity combinations are used. That is, the four polarity
combinations may be in any order in one cycle. An exemplary pattern
other than that of FIG. 8 is shown in FIG. 11.
[0079] Further, the above arrangement includes eight display frames
in one cycle (i.e. four combinations of right and left eye images);
however, four drive voltage polarity combinations may be used in
any number of display frames that is a multiple of 8. In such
implementations, the number of occurrences of each polarity
combination must be equal in one cycle formed of a number of
display frames that is a multiple of 8.
[0080] (Effects of Embodiment)
[0081] As described above, in the present embodiment, the polarity
control unit 23 controls the drive voltage polarity such that the
drive voltage polarity combination is changed at an interval of a
pair of display frames for right and left eye images. The polarity
control unit 23 controls the drive voltage polarity such that the
drive voltage polarity combinations, each in one pair of display
frames, include all the four polarity combinations in one cycle of
changes in the polarity composed of eight display frames, i.e. four
consecutive pairs of display frames.
[0082] This will prevent image sticking in the liquid crystal
caused by imbalances in the drive voltage in terms of polarity and
even up the distortion of the response waveform of the liquid
crystal in one cycle composed of eight display frames. Thus, the
arrangement of the present embodiment will prevent image sticking
in the liquid crystal and improve the display quality of 3D
images.
[0083] Moreover, as one cycle of changes in the drive voltage
polarity includes eight display frames, the operational load of
controlling the drive voltage polarity will be minimized.
[0084] Typically, the imbalances in the response waveform of the
liquid crystal may be rectified by applying a voltage that is
larger than the voltage necessary to drive the liquid crystal (i.e.
an overshoot voltage). With this method, if there are variations in
the amount of change in the voltage accompanying changes in the
drive voltage polarity, the correction voltages for these
variations must be stored in a memory or the like in the form of
data, requiring more memory space. In contrast, the arrangement of
the present embodiment will even up the variations in the amount of
change in the voltage, eliminating the necessity to store data of
correction voltages for the variations in the amount of change in
the voltage and thereby preventing an increase in memory space.
Other Embodiments
[0085] Although an embodiment of the present invention has been
described, the above embodiment is merely an example that may be
used to carry out the present invention. Thus, the present
invention is not limited to the above embodiment and the above
embodiment may be modified as necessary without departing from the
spirit of the invention.
[0086] In the above embodiment, the stereoscopic glasses 30 are
used to allow the viewer to perceive right and left eye images,
displayed in an alternating manner, as 3D images. However, any
arrangement for allowing the viewer to perceive right and left eye
images displayed in an alternating manner as 3D images may be
employed.
[0087] In the above embodiment, the liquid crystal display device 1
displays two frames for an identical right eye image and two frames
for an identical left eye image. However, the liquid crystal
display device 1 may display one frame for a right eye image and
one frame for a left eye image. In such implementations, each frame
for a right or left eye image constitutes a display frame.
INDUSTRIAL APPLICABILITY
[0088] The display device according to the present invention is
useful as a display device including a display panel that is
capable of displaying a right eye image and a left eye image in an
alternating manner.
* * * * *